The present invention relates to a DC/DC converter of the type having a transformer whose primary winding current is controlled by a transistor connected to a discharge circuit containing a choke, a diode and a capacitor. The secondary winding of the transformer supplies an output voltage to a load by means of a grid consisting of a rectifier diode, a free-running diode and a storage choke. Such converters are known for example from J. Wustehube, "Schaltnetzteile" ("Switching Grid Components"), expert-Verlag, 2nd. edition, 1982, p. 81, FIG. 2.23.
In these types of converters, during the conducting phase of the transistor the current of the transformer is transferred from the primary winding to the secondary winding and flows through the rectifier diode and the storage choke into the load connected to the outlet. In this process the current rises linearly in the choke and thus at the output. If the transistor is blocked, the rectifier diode is also in a blocking state and the free-running diode receives the decreasing current of the choke.
The magnetizing energy received by the transformer during the conducting phase flows, during the blocked phase, through a demagnetizing winding and the discharge diode back into an inlet capacitor. However, prior to the conduction of current by the demagnetizing winding, a steep rise of the collector-emitter voltage occurs and can cause an overshoot voltage, depending on the level of the collector current, the parasitic inductances between the primary and the secondary windings, and the switching velocity of the transistor.
To attenuate these undesirable effects, RCD or RC loading of the transistor has been used.
In the operation of such a converter, for example with a battery as the input source, the turn ratio of the windings must be designed for the lowest battery discharge voltage. In the case of high currents, high transmission frequencies and low output voltages the switching times of the diodes can no longer be neglected so that the duty factor must be V.sub.T eff &lt;0.5 and is frequently set at V.sub.T MAX =0.45 (See Wustehube, p. 64, before .sctn.2.9).
The disadvantages of the known configurations follow from the above. More particularly, due to the low maximum duty factor of V.sub.T =0.45 at relatively low values for the ratio K of windings in the primary and secondary windings in the transformer (K=2 . . . 3), and with higher power outputs of the converter (P.sub.W &gt;100W), high collector switching currents occur and in the case of bipolar transistors there are turn-off losses.